Harold w



Apri@ 22 @19% I 1,491,357 H. 3N. NICHLS A /sEcRET SIGNALING Filed Dec. 13. 1%?0 Tmmww L@ @las Fig.

. would accordingly result.

` nanou) w. menons, or raartnvvooig new JERSEY, Assrenon To Wns'rnniv ELEC- raro coureur, inconrona'rnn, or naar Yoan, n. Y., a CORPORATION or NEW YORK.

amusante `inea .recenter useful Improvements in Secret Signaling, of

which the 'fo'llorving'isa fuil,jcl `ear, concise, and exact 'description'.

riihis vinvefnti-o`n' relates to secretvv signaling, and in particular .to 'a 'secret signaiing 'sys- `tem wherein thefsignals 'are transmitted in the-form o-a' complex Wave'- which can be resolved .intel series' of vvttaves'havingl tref quencies. comprised Within;- 'a given ranger An object'oi the 'invention is to vso transniit a signal as to render' it incapable 'of intelligibleA` reception ord-inarynieans.

in accordance with a feature of the inven-v tion,`the transmitted signal is confused by the transpositioro portions of thesignal wave. atV the transmitting station and A-is'restored to its initial vcondition att-he receiving station. v

rEhe system to'iv'hiciithe invention is ap f' 'pliedr-may be classed with those secret sysg' tenis wherein thetransmitted signal is confused, as distinguished 'from those systems wherein means are provided for etiectually preventing the reception of the signal irnpulses.

It is readily apparentfrorn a; study of the record traced by the voiceA actuated vibrations of a telephone diaphragm that the vi brations making up the complex Wave -forml ot.' a voice Wave ohcy no regular or systematic sequence. They are indeed so confused and inter-mingled that .if the vibrations com- .prised Within va relatively small portion of the total frequency .range.usedl are eliminated the ecct is found to be repeated in manyparts of the record-With attendant decrease' in clearuess of rcceivedvoice signals in the case that the voice variations are transmitted and received by any of the known means. It' tl\c vibrations arctransmitted as electro- 'magnetic impulses and- .passed through a telephone receiver, uninteilgible signals .It is essentially' in this feature that the element of secrecy inhercs in the present` invention, aswell as `in the examples given. in 'one known system, the signal range is divided into two 1e, lean. semi no. 430,403.

parts, either of which alone is incapable of effecting intelligible Signals. The two parts of thesignal wave are separately transmitted as modulations of carrier wave which may .have the same or different frequencies. In another system, the essential principle is pre served by effecting a systematic change of -V each frequency-by subtracting the Voice frequencies from. a frequency larger than any component frequency of the voice wave, the effect being in the nature of a reversal of frequencies,the greatest frequency becoming thesmallesn-etc., the median frequency remaining unchanged. rccording'to the resent invention, the frequencies correspon ing' to a definite por- 'tion of the speech frequency band or spectrum are' transposed to .frequencies which may be outside the range of audition, or two portions maybe transposed asa whole so that each occupies the range previously occupied by the other; I In either case the resulting wave is used to modulate a single carrier Wave as in the usual vsystem as will be described later. by means of voice modulatedcarrier Waves as in 'the usual case, but the voice currents are impressed on the input-circuit of the modulating device in .two or more parts to each of' which is confined the currents of 'frequencies 'corresponding to a definite and predetermined. portion of the frequency "range used. There is also provided a means such, for example, as frequency converter or translator for changing each'of the -voice frequencies transmitted through the circuit by a 'predetermined amount.. in the particu-lar case in whichthe voice currents are transmitted yto the modulator through two circuits the frequencies corresponding to one circuit may be increased or decreased, de pending on which circuit contains the means inen`tioued,i by a predetermined amount. 'This change-Would be suii'cient to enlise the l. frequencies so changed to occupy a band or portion of the voice frequency range adjacent to and at the remote side of the band or lportion occupied by the frequency corn- The signal is transmitted Aponente transmitted 1n the other circuit. The

.Sii

definite amount and would he combined with the carrier wave and transmitted exactly as in the usual case. An. interceptor, however, who attempted to receive the ware and detect itin the ordinariv manner would derive a wave form identical with the. wave inipressed on the input. circuit of the moda lator. which wave could. not produce an intelligible signal when caused to actuatc the diaphragm of a telephone receiver. lThe. result would he. similar il' a portion of the frequency range was transposed to such a position that the resulting frequency hand was not continuous or of the saine width as the original voice frcquenc),v band. It' the voice currents were transmitted` to the modulator through more than two circuits and transposition were eliectcd in more than one" circuit, a confusion would also ensue, al though the result obtained in this case prohably would not justify the elaborate means required.

In order to make the system as described effective for transmission of intelligible siggnals to a desired station. a particular' means must he employed at, the receiving' station to recast the confused signal wave received at the. said station into an intelligible torni. This recastincr means is preferably similar to the, means employed at the transmitting station to confuse the signal and in ell'ect' acts on. the received signal wave in an inverse sense so as to restore the transposed portion of the frequency hand to its orie'inai trequency position. Accordingly the receiving circuitresemhles the transmittingr circuit in that it has the same number of similari)v related elements although the sequence otl operations is in general in inverse order. The, modulated carrier wave is deniodulated in the usual manner, the resultingr ware ot suhstantially audible 'trequencv being unintelli gible. rihis wave is transmitted to an amplifier and to the detecting device in two or more channels` or circuits in one or more of which is a frequency changing: means, such,v for example. as a frequency converter or translator which restores the, dill'crcnt frequency components to their initial frequency relation. the coniloined or resultant ware licing: identical with the original 'voice wave and capable of reprtuluction as an z'u'oustic wave in the usual telephone receiver.

For fui-thin' details ot the speciic features of the invention. reference is made to the 'following description which. taken in con-` nection with the drawing, discloses the invention in a preferred embodiment. in the drawing Fie'. l shows the .trarsniittiagrl circuits and'lfig. shows the receiving circuits of a' systeni embodying `the invention. Similar parts are indicated by similar refl erence symbols. the particular parts being' di'erentiated hy subscripts. The ordinals used have been chosen so as to indicate the casi device or circuit designated. .For example, modulators are shown h r the letter iii, do tectors hy D, high pass lilters by FH, etc.

Referring to l. .iii designates a ino-du.- latorgshown here as a three elen; .nt tuhe, although any one ot' the inanjY alternative circuits for accomplishing the niodulat w function.. or eren a mechanical metlulatinj),n means, mag.-v equally nell he used. This modulator serresto combine wates correspondingh to speech trefjucncy with the high frequency Ier wave. The carrier wares are inuit-esseci. on thr input circuit. of the modulator hy means ot the high frequency carrier .source through transformer "5 'ihr .vafes of voice .frctniencv are iinxn'essed on the input circuit livr "t,-rnier 'il two d'` et portions which arc derived ii;

common "from transformen if and separate uw ni'i to ttain.i'ormer tion passing through and the other throt i i more 'tuti-.f :tp-

troiu cans e i id i. Filters in an analogous of are descrihefl ir.

ot the `general tvt tfamphcll Tatent bio. The terms pass liltcr." ".lt.\\ A iltern and band Miter" are here used to describe respecthfcljv.. :i ilter which is d: tened to trans mit only currents haring ttiinzcncies above a predetermined limiting' ireoucncy called the "cuvoti' fretutencjf a. litter which is designed to transmit l'rctgucncies below the predetermined cnt-oli" i currency.y and a iiiter so designed as to t ansmit; currents havin#u 'frequencies between upper and .lowtzr cut-oi' frequencies.

The currents of frequencies transmitted through filter FL are changed. either def creased or increased, hy a. fixed amount. hy means or a` device here shown as fre-clue: fr translator or modulator althot-1gh-other means such. for example. as an indtc ion its function i., to

it i tran.-

:nodulator and trans as 'a series or viiorstions Within s of requencies, but is applicable to i transmission inA ssystem wherein types oig signsls may he transmitted. should also loe understood that the inven in its broadest aspect resides in the position of a portion, or portions of the tions corresponding to the signals ner in tre sequenos'oi opera-tions before were has heen combined with the v supplied by generator G or in one of iin l,idc bands' o5 the Wave resulting 'from lotion by device .The receiving its may .remain unchanged, it being also ry to suppress the remaining side et the trsnsmitting station.

ut is claimed i 1he method of secret carrier current ich fhony which. comprises the steps off dithe voice wave into two or more por i, chsnging each of the frequency oomrs included in one or more, but not all, :.d portions oy a sutlicient amount to scid ltmcniency components to occupy nwe of frequencies not previousiyousnsmitting the resultant wave ttions of aoarrier were, detecting said luted wave, snd restoring the voice ponentot the detected Wave to its initial ntion.

The method of secret carrier current ony which includes the steps ct modby dividing it into two he voice w ave giants, changing the frequency comente in one or more but not all of said by modulating with a frequency com- '3 corresponding to desired change tlieresfter suppressing' all but one side or the resultant wave, transmitting the ed and unchanged portions of the voice es modulations et the high 'frequency nfziveidetecting the transmitted end restoringy the voice component coi to its initial i'orm. 'liie method ot secret carrier current hony which includes the steps of modir the Voice wave oy dividing it into two ore parts, changing the frequency commts included in one or more, lult not all,

nl ports in; modulating with a 'ire- 1y component correspoiuling io the decliange and thereafter suppressing uit one side hand the result- "uve, transmitting the voice wave, inchanged t Auency components,

lotions ot digli frequency cer- ""ecting said wave, and r4 le i' fe compr-,nent thereof to im hy modulatingthe changed liref'omponeuts thereof with Wave equency equal to the said change o' the treqiu; cy hand which corn ocre" ce.

n ai

nai/c signaling sysjior d'viding the signer weve into two or more parts, means for transposing the frequency components included in one or more, but not all, of said parts, a modulating device for combining the changed and unchanged parts of the signal Wave With a high frequency carrier Wave, means for transmitting the resultant modulated Wave, means for receiving and detecting the transmitted Wave, means for sclecting the signal component from the product of the detecting means, and means tor restoring said signal Wave to its initial condition.

E. In a voice frequency signaling system, in combination means for dividing the voice frequency band into a plurality of ranges, means for changing the requencies in certain of the ranges While maintaining the 'frequencies 'of the remaining ranges constant, to produce e resultant ent in character from the original voice range', sind means for transmitting energy corresponding to the. resultant band.

5. lin "a secret carrier Wave telephone systern, means for generating a complex wave having speech characteristics, band filters 'for dividing said wave into two or more arts, means .in circuit with one or more of the band filters for changing by a predetermined amount the frequency components transmitted by said ilters, means for modulating a high requency carrier Wave in sccordance with the changed and unchanged parts of said complex Wave, means for transmitting the resultant modulated Wave, means for detecting the transmitted Wave, hand filters for selecting and transmitting the currents of modulating frequencies resulting from said detection, and means in circuit with one or more of the last mentioned hand filters for restoring the moduloting current wave to a form similar to that or' the original complex Wave.

'l'. The system as defined in claim G in which the said neans in circuit with said hand filters for changing the frequency components and for restoring the vmodulating current Wave consists in each instance of the combination of a modulating device. thc modulating frequency of which equals the desired frequency change, with va bund filter designed .for 'transmitting a single side hand of the output thereof.

8. The method of secret telephony which consists in dividing thc voice wave in two or more `portions, changing the frcquoncies'in certain of the `portions while maintaining 'the frequenza' in other portions constant, to produc-c a resultant distorted voicel wave, and transmitting energy corresponding to the distorted wave.

il. 'lfho method of secret telephony which conrrisos the steps of dividing the voice were into two portions, operating on the 'frequency vcompcments otliat portion which band of waves diien4 iiioiiicies tiie'iowfei frequencies to cause them occupy e position in the frequency scie medioieiy above and adjaeeiic to iie; oo eiipied 'by ehe otiieiportion, treiismi'ztiiigg diie 1voice 'weve so changed, and ieeioriig iiie feequencies to heii iniiiei eiation et, the ieceiving station.

EAG. The method of secret carrier current eiezohony 'which coiiipi'ises the siepe of .ividing @he infami of fi'equenciee conigii'isec'i ivihin lhe 'voice weve info two portions, sepping up the frequencies in the iower por! tion to e, corresponding position immeoii oitely above the frequencies of the oher por tion byfmodaiating with a cuiien having o frequency corresponding to the desired change and thei'eeiiei reeining oisiy *che up f side bead, transmitting the'oice :ireu fiieiicies so changed? es moiiulleione of e, high frequency cerisier 'waive9 fieecimg wie;

Fifi

weve, and estoiing the voice comjooinen of 'die detecting operation' to its initiai ccndi ion.

A. sigiiaiing system, wherein are io be ieseive epeecii signals iepi'csenied by bends L 'frequencies each divided into sub-bands, iiequeiicies of certain subbands being changed and the frequencies of the remainsub-bancs of a "band being unchaoged, having in combination means for selecting he changed and unchanged-frequency subioamis, means for restoring the sub-bands io their initial relation within the speech range, and o receiver responsive to such restored frequency sub-bands.

in witness whereof hereunto subscribe my neme this 1st day of December, A. ED. i920'.

HAROLB W. NCHLS. 

